Computer readable medium encoded with a program for fabricating 3d integrated circuit device using interface wafer as permanent carrier

ABSTRACT

A computer readable medium is provided that is encoded with a program comprising instructions for performing a method for fabricating a 3D integrated circuit structure. Provided are an interface wafer including a first wiring layer and through-silicon vias, and a first active circuitry layer wafer including active circuitry. The first active circuitry layer wafer is bonded to the interface wafer. Then, a first portion of the first active circuitry layer wafer is removed such that a second portion remains attached to the interface wafer. A stack structure including the interface wafer and the second portion of the first active circuitry layer wafer is bonded to a base wafer. Next, the interface wafer is thinned so as to form an interface layer, and metallizations coupled through the through-silicon vias in the interface layer to the first wiring layer are formed on the interface layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of prior U.S. application Ser. No.12/194,198, filed Aug. 19, 2008, now U.S. Pat. No. ______. The entiredisclosure of U.S. application Ser. No. 12/194,198 is hereinincorporated by reference.

Additionally, this application is related to application “3D IntegratedCircuit Device Fabrication With Precisely Controllable SubstrateRemoval,” Ser. No. 12/194,065, now U.S. Pat. No. 8,129,256, andapplication “3D Integrated Circuit Device Having Lower-Cost ActiveCircuitry Layers Stacked Before Higher-Cost Active Circuitry Layer,”Ser. No. 12/194,211, now U.S. Pat. No. ______. These relatedapplications are incorporated herein by reference in their entirety.

This invention was made with Government support under Contract No.:N66001-04-C-8032 awarded by Defense Advanced Research Projects Agency(DARPA). The Government has certain rights in this invention.

FIELD OF THE INVENTION

The present invention generally relates to the field of integratedcircuits, and more particularly relates to the fabrication ofthree-dimensional (3D) integrated circuit devices.

BACKGROUND OF THE INVENTION

Three-dimensional (3D) integrated circuit devices are experiencingextremely active development in the industry. One problem experienced inthe fabrication of 3D integrated circuit devices is that general purposesubstrate thinning techniques do not allow the final substrate to beproduced with a controlled thickness that is thin enough to allowhigh-density through-silicon vias with reasonable aspect ratios to berealized. One known technique for overcoming this problem is utilizing aburied oxide layer (BOX) as the etch stop. However, this technique onlyworks for silicon-on-insulator (SOI) wafers. Further, even with an SOIwafer, this technique does not work for SOI circuits having structuresthat extend below the buried oxide, such as an embedded DRAM (e-DRAM)trench.

Another known technique for overcoming this problem is utilizing adouble buried oxide layer (double-BOX) structure. However, thistechnique greatly increases the manufacturing cost. Further, like thesingle buried oxide layer structure solution, the double-BOX techniquerequires protection of the substrate from the other wafer. Suchprotection is required because, while the SOI wafer acts as an etchstop, it does not provide selectivity between the different substrates.

Yet another known technique for overcoming this problem is to not use anetch stop but to perform “blind” thinning. However, this technique doesnot allow the wafers to be thinned aggressively and creates uniformityproblems. Further, for integrated circuits that require a high densityof 3D vias, this technique also forces the use of high aspect ratio viasthat cannot be filled with copper. Instead, tungsten has to be used forthe vias, which has three times higher resistivity than copper.

Another problem experienced in the fabrication of 3D integrated circuitdevices is that stacking three or more layers to create a multi-layerstack leads to yield loss. One technique that attempts to overcome thisproblem is to stack layers through bonding to temporary handle wafers.However, the use of such a temporary handle wafer (e.g., a glass wafer)induces overlay distortions that degrade the alignment overlay betweenthe wafers. That is, this technique does not allow high-precisionoptical alignment in subsequent lithographic steps. Withouthigh-precision optical alignment, the via density is degraded and largecapture pads with high parasitic capacitances must be used. Further, theuse of such bonding to temporary handle wafers does allow flexibility inthe way the wafers are stacked.

Another technique that attempts to overcome this problem is to simplyuse a direct face-to-face joining of the wafers. However, such directface-to-face joining is problematic because the bottom wafer (whichusually is a logic wafer) must then be used as the handle waferthroughout the stacking process. While this may be acceptable in thefabrication of a two layer stack, for a multi-layer (i.e., three or morelayer) stack this means that the logic wafer must go through manybonding and thinning steps. This increases the probability ofcatastrophic failure and loss of the entire integrated circuit,including the logic wafer that is often the most expensive wafer in thestack.

SUMMARY OF THE INVENTION

One embodiment of the present invention provides a method forfabricating a 3D integrated circuit structure. According to the method,an interface wafer that includes a first wiring layer andthrough-silicon vias is provided. A first active circuitry layer waferthat includes active circuitry is provided, and the first activecircuitry layer wafer is bonded face down to the interface wafer. Then,a first portion of the first active circuitry layer wafer is removedsuch that a second portion of the first active circuitry layer waferremains attached to the interface wafer. A base wafer that includes asecond wiring layer is provided, and a stack structure is bonded facedown to the base wafer. The stack structure includes the interface waferand the second portion of the first active circuitry layer wafer. Next,the interface wafer is thinned so as to form an interface layer, andmetallizations are formed on the interface layer. The metallizations arecoupled through the through-silicon vias in the interface layer to thefirst wiring layer.

Another embodiment of the present invention provides a tangible computerreadable medium encoded with a program that comprises instructions forperforming such a method for fabricating a 3D integrated circuitstructure.

Other objects, features, and advantages of the present invention willbecome apparent from the following detailed description. It should beunderstood, however, that the detailed description and specificexamples, while indicating preferred embodiments of the presentinvention, are given by way of illustration only and variousmodifications may naturally be performed without deviating from thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 11 are cross-sectional views of a process for fabricating athree-dimensional integrated circuit device according to one embodimentof the present invention;

FIG. 12 shows a 3D integrated circuit structure having a logiclayer-active circuitry layers-interface layer stack structure accordingto one embodiment of the present invention;

FIG. 13 shows a 3D integrated circuit structure in which all of thelayers are SOI wafers in accordance with one embodiment of the presentinvention;

FIG. 14 shows a 3D integrated circuit structure having circuit elementsin the interface layer of the stack structure according to oneembodiment of the present invention; and

FIG. 15 is a flow diagram of a design process used in semiconductordesign, manufacture, and/or test.

DETAILED DESCRIPTION

Preferred embodiments of the present invention will be described indetail hereinbelow with reference to the attached drawings.

Embodiments of the present invention use the interface wafer as apermanent carrier during three-dimensional (3D) integrated circuitdevice fabrication. In one exemplary embodiment, the interface wafer isused during the stacking of the layers as a carrier for all of thelayers of the stack except the base wafer. Thus, there is no need forlayers to be bonded to temporary handle wafers. After the layers arestacked and attached to the base wafer, this carrier (i.e., interfacewafer) is not discarded, but instead permanently remains as theinterface between the stacked layers and the package in the 3Dintegrated circuit device. For example, in this exemplary embodiment theinterface wafer has through-silicon vias at the same pitch as thepackage, and redistribution wiring that re-routes the leads to interfacewith the bottom layer in the stack. Thus, the present inventionovercomes the problems that occur when forming a stack of layers usingtemporary handle wafers.

FIGS. 1 to 11 illustrate a process for fabricating a three-dimensionalintegrated circuit device according to one embodiment of the presentinvention. As shown in FIG. 1, the process starts with an interfacewafer 100, which will be the interface between the stacked activecircuitry layers and a package in the completed integrated circuit. Inparticular, the exposed surface of the interface wafer 100 will carrythe C4 (controlled collapse chip connection) solder bumps in thecompleted integrated circuit. These C4 (or flip-chip) solder bumps areused to attach the integrated circuit to the package (e.g., a resin orceramic module). The interface wafer 100 is a substrate made of amaterial that is not soluble in the etchants that are utilized in thesubsequent substrate removal steps (i.e., a material that is not solublein etchants that selectively etch P+ layers with respect to P− layers).

In this embodiment, the interface wafer is not formed from a P+substrate, so it is impervious to the etching that removes thesubstrates of the wafers of the active circuitry layers of the stack.The interface wafer 100 is a silicon substrate that has through-siliconvias 102 at the same pitch as the package. In this embodiment, thedepths and sizes of the vias in the interface wafer are different thanthose of the vias in the other wafers. Further, in this embodiment, thethrough-silicon vias are filled with tungsten metal. In furtherembodiments, the through-silicon vias are filled with othermetallurgies, such as copper. The through-silicon vias of the interfacewafer 100 do not need to be made of the same material as thethrough-silicon vias in the other layers of the stack. The interfacewafer 100 also has a wiring layer 104 that distributes signals and powerto the stacked layers of the integrated circuit. In this embodiment, theinterface wafer 100 is transparent to infrared radiation.

Additionally, a first active circuitry layer wafer 200 is provided. Thefirst active circuitry layer wafer 200 is formed with a P+/P− siliconsubstrate, which is a P+ wafer 202 that has a P− top active circuitrylayer 204. In this embodiment, the P− top active circuitry layer 204 isgrown epitaxially on a P+ wafer and has a thickness of between about 5and 20 microns. Further, in this embodiment the P+ wafer is aboron-doped wafer with a doping concentration in the range of about1×10¹⁸ cm−³ to 3×10²⁰cm−³, and the P− epitaxial layer has a dopingconcentration of less than about 1×10¹⁸cm−³. In further embodiments, theP− epitaxial layer is not-intentionally-doped, or doped N-type with aconcentration of less than about 1×10¹⁸cm−³.

Through-silicon vias 206 are etched into the P− top active circuitrylayer 204 so as to end near the P+ wafer 202. In further embodiments,the vias 206 pass through the surface of the P+ wafer 202. In thisembodiment, the through-silicon vias are filled with copper. In furtherembodiments, the through-silicon vias are filled with othermetallurgies. Active circuitry (i.e., active components such astransistors) and one or more wiring levels 208 are formed at the topsurface of the first active circuitry layer wafer 200.

Next, as shown in FIG. 2, the first active circuitry layer wafer 200 isaligned face down to the interface wafer 100. This face-to-facealignment using two silicon wafers allows for higher-precision alignmentcompared to the case where one of the wafers utilizes a temporary handlewafer (e.g., of glass). The first active circuitry layer wafer 200 isbonded to the interface wafer 100, so that the interface wafer functionsas the permanent carrier for the first active circuitry layer. In thisembodiment, copper-copper or a combination of copper-copper and adhesivebonding (e.g., using a polymer adhesive) is utilized. In furtherembodiments, other metallurgies (such as a copper alloy or a nickel-goldalloy) are utilized.

The P+ layer 202 of the first active circuitry layer wafer 200 is thenselectively removed, as shown in FIG. 3. In this embodiment, a series ofnon-selective substrate thinning processes are first utilized (e.g.,wafer grinding and polishing), and then wet chemical etching is utilizedto remove the remaining P+ layer 202 selectively with respect to the P−layer 204. The final removal of the P+ layer 202 of the first activecircuitry layer wafer 200 is performed using a selective etchant, suchas HNA (hydrofluoric acid/nitric acid/acetic acid). Because the bulk ofthe interface wafer 100 is not soluble in this selective etchant, theprocess is very robust. Additionally, in this embodiment the interfacewafer 100 is made from a lightly doped N− or P− silicon in order toallow infrared (IR) alignment to be performed. In other embodiments, theinterface wafer 100 is also a P+ silicon substrate.

This selective removal of the P+ layer does not substantially affect theP− epitaxial layer 204, the active circuitry and wiring levels 104 and208, or the interface wafer 100 that remain. Thus, the use of the P+/P−substrate allows the P+ layer to be selectively removed, so that thewafer is controllably thinned to the thickness of the P− layer, whichcan be made very thin (e.g., about 5-20 microns thick).

Next, in this embodiment, an etch back (e.g., using reactive ionetching) is performed in order to expose the top portions of the vias206 in the P− layer 204. In other embodiments in which the vias 206 passinto the P+ layer 202, such an etch is not needed as the top portions ofthe vias are already exposed after the selective removal of the P+layer. A wiring layer 210 having insulation and one or more back end ofline (BEOL) metallization layers coupled to the vias 206 is thenpatterned onto the backside of the P− layer 204, as shown in FIG. 4. Inthis embodiment, each metallization layer of the wiring layer 210 isformed by depositing a dielectric layer, etching the dielectric layer,and depositing metal in the etched areas.

These steps are then repeated any number of times to create amulti-layer stack on the interface wafer 100, with the interface waferfunctioning as the permanent carrier for this stack. For example, in theillustrated embodiment these steps are repeated once more to create asecond active circuitry layer. More specifically, a second activecircuitry layer wafer 300 is provided, as shown in FIG. 5. The secondactive circuitry layer wafer 300 is also formed with a P+/P− siliconsubstrate, which is a P+ wafer 302 that has a P− top active circuitrylayer 304. In this embodiment, the P− top active circuitry layer 304 isgrown epitaxially and has a thickness of between about 5 and 20 microns.Through-silicon vias 306 are etched into the P− top active circuitrylayer 304 so as to end near the P+ wafer 302, and active circuitry andone or more wiring levels 308 are formed at the top surface of thesecond active circuitry layer wafer 300.

Next, as shown in FIG. 6, the second active circuitry layer wafer 300 isaligned face down to the wiring layer 210 on the first P− layer 204attached to the interface wafer 100. This face-to-face alignment usingtwo silicon wafers allows for higher-precision alignment compared to thecase where one of the wafers utilizes a temporary handle wafer (e.g., ofglass). The second active circuitry layer wafer 300 is bonded to thewiring layer 210 using copper-copper or a combination of copper-copperand adhesive bonding, so that the interface wafer functions as thepermanent carrier for the first and second active circuitry layers. Infurther embodiments, other metallurgies (such as a copper alloy or anickel-gold alloy) are utilized.

The P+ layer 302 of the second active circuitry layer wafer 300 is thenselectively removed, as shown in FIG. 7. In this embodiment, a series ofnon-selective substrate thinning processes are first utilized (e.g.,wafer grinding and polishing), and then a wet chemical etching isutilized to remove the remaining P+ layer 302 of the second activecircuitry layer wafer 300 selectively with respect to the P− layer 304of the second active circuitry layer wafer 300. This selective removalof the P+ layer 302 of the second active circuitry layer wafer 300 doesnot substantially affect the P− layers 204 and 304, the active circuitryand wiring levels 104, 208, 210, and 308, or the interface wafer 100that remain. Thus, the interface wafer 100 is robust against multiplesubstrate removal etches for removing the P+ layers of all of the activecircuitry layer wafers that are used to create the multi-layer stack.

An etch back is then performed in order to expose the top portions ofthe vias 306 in the second P− layer 304. A wiring layer 310 havinginsulation and one or more BEOL metallization layers coupled to the vias306 is then patterned onto the backside of the second P− layer 304, asshown in FIG. 8.

After the desired number of active circuitry layers are bonded togetherin this manner with the interface wafer functioning as the permanentcarrier for the stack of active circuitry layers, the resultingstructure is attached to a base wafer 800, as shown in FIG. 9. The basewafer 800 of this embodiment is made of bulk silicon or SOI and istopped by a wiring layer 808 having insulation and one or more BEOLmetallization layers. In this embodiment, the base wafer 800 does nothave through-silicon vias. In some embodiments, the base wafer includesactive circuitry (e.g., transistors) and/or passive circuit elements(e.g., resistors and capacitors). With the interface wafer 100functioning as the permanent carrier for the stack, the interface waferand the stack of active circuitry layers attached to it are aligned facedown to the base wafer. Thus, because they have been “flipped” twice inthis embodiment, all of the active circuitry layers that were previouslystacked on the interface wafer 100 are now face up with respect to thebase wafer 800, as shown by the arrows in FIG. 9.

The top wiring layer 310 of the multi-layer stack is then bonded to thebase wafer 800. In this embodiment, copper-copper or a combination ofcopper-copper and adhesive bonding (e.g., using a polymer adhesive) isutilized. In further embodiments, other metallurgies (such as a copperalloy or a nickel-gold alloy) are utilized. The permanent carrier (i.e.,interface wafer) is then processed so as to remain as the interfacebetween the stacked layers and the package in the 3D integrated circuitdevice. In particular, the interface wafer 100 is thinned. In thisembodiment, this thinning is achieved in two steps. First, a combinationof wafer grinding and polishing are performed to thin the interfacewafer to above the vias 102 in the interface wafer 100. Then, theinterface wafer 100 is further thinned through a dry etch (e.g., usingreactive ion etching) so as to form an interface layer 101 that exposesthe top portions of the vias 102, as shown in FIG. 10. A backsidedielectric layer 820 is then deposited onto the backside of theinterface layer 101.

As shown in FIG. 11, the backside dielectric layer 820 is then polishedand/or etched, and contact metallizations 822 are deposited onto thevias 102 of the interface layer 101. In this embodiment, a simpleball-limiting metallization is deposited on the vias so as to allowdeposition of C4 solder bumps. In other embodiments, more complexdielectric and metallization layers are formed. The C4 solder bumps 825are then deposited onto the contact metallizations 822 to complete the3D integrated circuit structure. In this embodiment, the C4 solder bumpsare on the order of 100 μm in diameter and 200 μm or less in pitch.These C4 (or flip-chip) solder bumps are then used to bond theintegrated circuit to the package (e.g., a resin or ceramic module).

The exemplary process described above is only meant to illustrate theprinciples of the present invention. By simply varying the number,types, and order of layers that are stacked on the interface wafer, manydifferent 3D integrated circuit structures can be produced. For example,while the exemplary process described above produces a structure havinga 1+2+1 stack (1 base wafer, 2 active circuitry layers, and 1 interfacelayer), a structure having a 1+N+1 stack can be created by simplyrepeating the active circuitry layer stacking process N times asdescribed above. In the 1+N+1 stack structure, additional activecircuitry layers (each analogous to the one formed by layers 210, 204,and 208) are stacked between layer 210 of the first active circuitrylayer and layer 308 of the last (N^(th)) active circuitry layer in thestructure of FIG. 11 (see, for example, FIG. 12).

Similarly, a structure having a 1+1+1 stack can be created by onlyperforming the active circuitry layer stacking process one time. In the1+1+1 stack structure, the second active circuitry layer (the one formedby layers 310, 304, and 308) is absent from the structure of FIG. 11.Thus, the process of the present invention for stacking multiple activecircuitry layers on top of a base wafer can also be used in a consistentmanner to stack only one active circuitry layer on a base wafer.

In further embodiments, a logic wafer (i.e., a wafer with logiccircuitry) is used as the base wafer (i.e., the base wafer includeslogic circuitry). For example, FIG. 12 shows a 3D integrated circuitstructure having a logic wafer-active circuitry layers-interface layerstack structure according to one embodiment of the present invention.This exemplary embodiment has an interface layer that is stacked on topof N active circuitry layers, which are memory layers, that are in turnstacked on top of a logic wafer. The memory layers are any type ofmemory, such as SRAM memory, e-DRAM memory, or a combination of the two.The logic wafer contains control and/or logic circuitry, such as amemory controller or a processor core. In another embodiment, theinterface layer and only one active circuitry layer (e.g., memory layer)are stacked on top of the logic wafer.

Additionally, one or more of the wafers used in the process describedabove can be a silicon-on-insulator (SOI) wafer. For example, FIG. 13shows a 3D integrated circuit structure in which all of the layers areformed on SOI wafers in accordance with one embodiment of the presentinvention. In an alternative embodiment, the base wafer is an SOIsubstrate (as in FIG. 13), while the wafers for the active circuitrylayers and the interface layer are bulk silicon wafers (as in FIG. 12).In yet another embodiment, the base wafer is an SOI substrate (as inFIG. 13), the wafers for the active circuitry layers include both an SOIwafer (as in FIG. 13) and a bulk silicon wafer (as in FIG. 12), and thewafer for the interface layer is either an SOI or bulk silicon wafer.

FIG. 14 shows a 3D integrated circuit structure having circuit elementsin the interface layer of the stack structure according to oneembodiment of the present invention. In this embodiment, the interfacelayer includes additional functionality through the provision of activecircuitry and/or passive circuit elements. For example, the interfacelayer can include a decoupling capacitor layer in order to stabilize thevoltage grid. Alternatively or additionally, the interface layer caninclude voltage regulation circuitry formed by active transistors aswell as passive elements such as decoupling capacitors.

Accordingly, embodiments of the present invention utilize use aninterface wafer as a permanent carrier during three-dimensional (3D)integrated circuit device fabrication. The interface wafer is usedduring the stacking of the layers as a carrier for all the layers of thestack, so there is no need for temporary handle wafers. This carrier(i.e., interface wafer) permanently remains as the interface between thestacked layers and the package in the 3D integrated circuit device.Thus, the present invention overcomes the problems that occur whenforming a stack of layers for 3D integration using temporary handlewafers. Further, this permanent carrier technique can be easily adaptedto different types of stacks, such as two-active-layer stacks andmulti-layer stacks.

The embodiments of the present invention described above are meant to beillustrative of the principles of the present invention. These devicefabrication processes are compatible with conventional semiconductorfabrication methodology, and thus various modifications and adaptationscan be made by one of ordinary skill in the art. All such modificationsstill fall within the scope of the present invention. For example, thevarious layer thicknesses, material types, deposition techniques, andthe like discussed above are not meant to be limiting.

Furthermore, some of the features of the examples of the presentinvention may be used to advantage without the corresponding use ofother features. As such, the foregoing description should be consideredas merely illustrative of the principles, teachings, examples andexemplary embodiments of the present invention, and not in limitationthereof.

It should be understood that these embodiments are only examples of themany advantageous uses of the innovative teachings herein. In general,statements made in the specification of the present application do notnecessarily limit any of the various claimed inventions. Moreover, somestatements may apply to some inventive features but not to others. Ingeneral, unless otherwise indicated, singular elements may be in theplural and vice versa with no loss of generality.

The circuit as described above is part of the design for an integratedcircuit chip. The chip design is created in a graphical computerprogramming language, and stored in a computer storage medium (such as adisk, tape, physical hard drive, or virtual hard drive such as in astorage access network). If the designer does not fabricate chips or thephotolithographic masks used to fabricate chips, the designer transmitsthe resulting design by physical means (e.g., by providing a copy of thestorage medium storing the design) or electronically (e.g., through theInternet) to such entities, directly or indirectly. The stored design isthen converted into the appropriate format (e.g., GDSII) for thefabrication of photolithographic masks, which typically include multiplecopies of the chip design in question that are to be formed on a wafer.The photolithographic masks are utilized to define areas of the wafer(and/or the layers thereon) to be etched or otherwise processed.

The method as described above is used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare chip, or in a packaged form. Inthe latter case, the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case, the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboard,or other input device, and a central processor.

FIG. 15 shows a block diagram of an exemplary design flow 900 used forexample, in semiconductor IC logic design, simulation, test, layout, andmanufacture. Design flow 900 includes processes and mechanisms forprocessing design structures or devices to generate logically orotherwise functionally equivalent representations of the designstructures and/or devices described above and shown in FIGS. 1-14. Thedesign structures processed and/or generated by design flow 900 may beencoded on machine-readable transmission or storage media to includedata and/or instructions that when executed or otherwise processed on adata processing system generate a logically, structurally, mechanically,or otherwise functionally equivalent representation of hardwarecomponents, circuits, devices, or systems. Design flow 900 may varydepending on the type of representation being designed. For example, adesign flow 900 for building an application specific IC (ASIC) maydiffer from a design flow 900 for designing a standard component or froma design flow 900 for instantiating the design into a programmablearray, for example a programmable gate array (PGA) or a fieldprogrammable gate array (FPGA) offered by Altera® Inc. or Xilinx® Inc.

FIG. 15 illustrates multiple such design structures including an inputdesign structure 920 that is preferably processed by a design process910. Design structure 920 may be a logical simulation design structuregenerated and processed by design process 910 to produce a logicallyequivalent functional representation of a hardware device. Designstructure 920 may also or alternatively comprise data and/or programinstructions that when processed by design process 910, generate afunctional representation of the physical structure of a hardwaredevice. Whether representing functional and/or structural designfeatures, design structure 920 may be generated using electroniccomputer-aided design (ECAD) such as implemented by a coredeveloper/designer. When encoded on a machine-readable datatransmission, gate array, or storage medium, design structure 920 may beaccessed and processed by one or more hardware and/or software moduleswithin design process 910 to simulate or otherwise functionallyrepresent an electronic component, circuit, electronic or logic module,apparatus, device, or system such as those shown in FIGS. 1-14. As such,design structure 920 may comprise files or other data structuresincluding human and/or machine-readable source code, compiledstructures, and computer-executable code structures that when processedby a design or simulation data processing system, functionally simulateor otherwise represent circuits or other levels of hardware logicdesign. Such data structures may include hardware-description language(HDL) design entities or other data structures conforming to and/orcompatible with lower-level HDL design languages such as Verilog andVHDL, and/or higher level design languages such as C or C++.

Design process 910 preferably employs and incorporates hardware and/orsoftware modules for synthesizing, translating, or otherwise processinga design/simulation functional equivalent of the components, circuits,devices, or logic structures shown in FIGS. 1-14 to generate a netlist980 which may contain design structures such as design structure 920.Netlist 980 may comprise, for example, compiled or otherwise processeddata structures representing a list of wires, discrete components, logicgates, control circuits, I/O devices, models, etc. that describes theconnections to other elements and circuits in an integrated circuitdesign. Netlist 980 may be synthesized using an iterative process inwhich netlist 980 is resynthesized one or more times depending on designspecifications and parameters for the device. As with other designstructure types described herein, netlist 980 may be recorded on amachine-readable data storage medium or programmed into a programmablegate array. The medium may be a non-volatile storage medium such as amagnetic or optical disk drive, a programmable gate array, a compactflash, or other flash memory. Additionally, or in the alternative, themedium may be a system or cache memory, buffer space, or electrically oroptically conductive devices and materials on which data packets may betransmitted and intermediately stored via the Internet, or othernetworking suitable means.

Design process 910 may include hardware and software modules forprocessing a variety of input data structure types including netlist980. Such data structure types may reside, for example, within libraryelements 930 and include a set of commonly used elements, circuits, anddevices, including models, layouts, and symbolic representations, for agiven manufacturing technology (e.g., different technology nodes, 32 nm,45 nm, 90 nm, etc.). The data structure types may further include designspecifications 940, characterization data 950, verification data 960,design rules 970, and test data files 985 which may include input testpatterns, output test results, and other testing information. Designprocess 910 may further include, for example, standard mechanical designprocesses such as stress analysis, thermal analysis, mechanical eventsimulation, process simulation for operations such as casting, molding,and die press forming, etc. One of ordinary skill in the art ofmechanical design can appreciate the extent of possible mechanicaldesign tools and applications used in design process 910 withoutdeviating from the scope and spirit of the invention. Design process 910may also include modules for performing standard circuit designprocesses such as timing analysis, verification, design rule checking,place and route operations, etc.

Design process 910 employs and incorporates logic and physical designtools such as HDL compilers and simulation model build tools to processdesign structure 920 together with some or all of the depictedsupporting data structures along with any additional mechanical designor data (if applicable), to generate a second design structure 990.Design structure 990 resides on a storage medium or programmable gatearray in a data format used for the exchange of data of mechanicaldevices and structures (e.g., information stored in a ICES, DXF,Parasolid XT, JT, DRG, or any other suitable format for storing orrendering such mechanical design structures). Similar to designstructure 920, design structure 990 preferably comprises one or morefiles, data structures, or other computer-encoded data or instructionsthat reside on transmission or data storage media and that whenprocessed by an ECAD system generate a logically or otherwisefunctionally equivalent form of one or more of the embodiments of theinvention shown in FIGS. 1-14. In one embodiment, design structure 990may comprise a compiled, executable HDL simulation model thatfunctionally simulates the devices shown in FIGS. 1-14.

Design structure 990 may also employ a data format used for the exchangeof layout data of integrated circuits and/or symbolic data format (e.g.,information stored in a GDSII (GDS2), GL1, OASIS, map files, or anyother suitable format for storing such design data structures). Designstructure 990 may comprise information such as, for example, symbolicdata, map files, test data files, design content files, manufacturingdata, layout parameters, wires, levels of metal, vias, shapes, data forrouting through the manufacturing line, and any other data required by amanufacturer or other designer/developer to produce a device orstructure as described above and shown in FIGS. 1-14. Design structure990 may then proceed to a stage 995 where, for example, design structure990: proceeds to tape-out, is released to manufacturing, is released toa mask house, is sent to another design house, is sent back to thecustomer, etc.

What is claimed is:
 1. A non-transitory computer readable medium encoded with a program for fabricating a 3D integrated circuit structure, the program comprising instructions for performing the steps of: providing an interface wafer, the interface wafer including a first wiring layer and through-silicon vias; providing a first active circuitry layer wafer including active circuitry; bonding the first active circuitry layer wafer face down to the interface wafer; after bonding the first active circuitry layer wafer, removing a first portion of the first active circuitry layer wafer such that a second portion of the first active circuitry layer wafer remains attached to the interface wafer; providing a base wafer, the base wafer including a second wiring layer; bonding a stack structure face down to the base wafer, the stack structure including the interface wafer and the second portion of the first active circuitry layer wafer; and after bonding the stack structure, thinning the interface wafer so as to form an interface layer, and forming metallizations on the interface layer, the metallizations being coupled through the through-silicon vias in the interface layer to the first wiring layer.
 2. The non-transitory computer readable medium of claim 1, wherein the program further comprises instructions for performing the steps of: providing another active circuitry layer wafer including active circuitry; bonding the other active circuitry layer wafer face down above the interface wafer and the second portion of the first active circuitry layer wafer; and after bonding the other active circuitry layer wafer, removing a first portion of the other active circuitry layer wafer such that a second portion of the other active circuitry layer wafer remains above the interface wafer and the second portion of the first active circuitry layer wafer, wherein the stack structure that is bonded face down to the base wafer also includes the second portion of the other active circuitry layer wafer.
 3. The non-transitory computer readable medium of claim 2, wherein the program further comprises instructions for performing the step of: repeating N times the steps of providing another active circuitry layer wafer, bonding the other active circuitry layer wafer, and removing a first portion of the other active circuitry layer wafer, wherein the stack structure that is bonded face down to the base wafer also includes the second portions of the N other active circuitry layer wafers.
 4. The non-transitory computer readable medium of claim 2, wherein the program further comprises instructions for performing the steps of: after removing the first portion of the other active circuitry layer wafer, fabricating another wiring layer on the second portion of the other active circuitry layer wafer; and repeating N times the steps of providing another active circuitry layer wafer, bonding the other active circuitry layer wafer, removing a first portion of the other active circuitry layer wafer, and fabricating another wiring layer, wherein in the step of bonding the stack structure face down to the base wafer, the wiring layer on the second portion of the Nth wafer is bonded face down to the base wafer.
 5. The non-transitory computer readable medium of claim 2, wherein the program further comprises instructions for performing the steps of: after removing the first portion of the first active circuitry layer wafer, fabricating a third wiring layer on the second portion of the first active circuitry layer wafer; and after removing the first portion of the other active circuitry layer wafer, fabricating a fourth wiring layer on the second portion of the other active circuitry layer wafer, wherein in the step of bonding the other active circuitry layer wafer, the other active circuitry layer wafer is bonded face down to the third wiring layer, and in the step of bonding the stack structure, the fourth wiring layer is bonded face down to the base wafer.
 6. The non-transitory computer readable medium of claim 1, wherein the program further comprises instructions for performing the step of: after removing the first portion of the first active circuitry layer wafer, fabricating a third wiring layer on the second portion of the first active circuitry layer wafer, wherein in the step of bonding the stack structure, the third wiring layer is bonded face down to the base wafer.
 7. The non-transitory computer readable medium of claim 1, wherein the interface wafer is formed of a material that is not soluble in an etchant used in the removing step to remove the first portion of the first active circuitry layer wafer.
 8. The non-transitory computer readable medium of claim 1, wherein the metallizations on the interface layer comprise solder bumps.
 9. The non-transitory computer readable medium of claim 1, wherein the first active circuitry layer wafer comprises a bulk silicon wafer.
 10. The non-transitory computer readable medium of claim 1, wherein the first active circuitry layer wafer comprises an SOI wafer.
 11. The non-transitory computer readable medium of claim 1, wherein the interface wafer comprises an SOI wafer.
 12. The non-transitory computer readable medium of claim 1, wherein the interface wafer further includes active circuitry and/or passive circuit elements.
 13. The non-transitory computer readable medium of claim 1, wherein the interface wafer further includes decoupling capacitors and/or voltage regulation circuitry.
 14. The non-transitory computer readable medium of claim 1, wherein the base wafer includes logic circuitry.
 15. A non-transitory computer readable medium encoded with a program for fabricating a 3D integrated circuit structure, the program comprising instructions for performing the steps of: providing an interface wafer, the interface wafer including a first wiring layer and through-silicon vias; providing a first active circuitry layer wafer including active circuitry and through-silicon vias; bonding the first active circuitry layer wafer face down to the interface wafer; after bonding the first active circuitry layer wafer face down to the interface wafer, removing a first portion of the first active circuitry layer wafer such that a second portion of the first active circuitry layer wafer remains attached to the interface wafer; after removing the first portion of the first active circuitry layer wafer, fabricating a second wiring layer on the second portion of the first active circuitry layer wafer; providing a second active circuitry layer wafer including active circuitry; bonding the second active circuitry layer wafer face down to the second wiring layer; after bonding the second active circuitry layer wafer face down to the second wiring layer, removing a first portion of the second active circuitry layer wafer such that a second portion of the second active circuitry layer wafer remains attached to the second wring layer; after removing the first portion of the second active circuitry layer wafer, fabricating a third wiring layer on the second portion the second active circuitry layer wafer; providing a base wafer, the base wafer including a fourth wiring layer; bonding the third wiring layer face down to the base wafer; after bonding the third wiring layer face down to the base wafer, thinning the interface wafer so as to form an interface layer, and forming metallizations comprising solder bumps on the interface layer, the solder bumps being coupled through the through-silicon vias in the interface layer to the first wiring layer; and bonding the solder bumps to a package.
 16. The non-transitory computer readable medium of claim 15, wherein the first active circuitry layer wafer comprises a bulk silicon wafer.
 17. The non-transitory computer readable medium of claim 15, wherein the first active circuitry layer wafer comprises an SOI wafer.
 18. The non-transitory computer readable medium of claim 15, wherein the interface wafer comprises an SOI wafer.
 19. The non-transitory computer readable medium of claim 15, wherein the interface wafer further includes active circuitry and/or passive circuit elements.
 20. The non-transitory computer readable medium of claim 15, wherein the base wafer includes logic circuitry. 